[PATCH] D35004: [DWARF] - Add API to allow DWARFContextInMemory to delegate relocations handling to client.

[Rafael Avila de Espindola via llvm-commits]

I wonder if it would not be better to split DWARFContextInMemory in two.

DWARFContextInMemory would have no idea how to get section contents and
relocations. It would deffer that to a helper object. The
DWARFContextInMemory constructor would do nothing.

In llvm we would have a helper implementation that looks just like the
current DWARFContextInMemory constructor:

* Walk all sections.
* Decompress if compressed.
* Parse relocations into maps.

In lld we could have a very different implementation

* Don't walk the sections. We already did that.
* Don't decompress, we already did that.
* Don't parse relocations early.

The last point is because lld does a very simple in order walk over the
data. I would be surprised if it is not more efficient to walk the
relocations is lockstep instead of having a full map.

Cheers,
Rafael

George Rimar via Phabricator <reviews at reviews.llvm.org> writes:

> grimar created this revision.
>
> Previously DWARFContextInMemory handled relocations by itself.
> (or used pre-relocated section content via another API)
> This patch adds way to delegate relocations handling to client for each
> relocation section.
>
> I am using it in patch for LLD to speedup .gdb_index building, will
> upload it and add dependency to this one really soon.
>
> That allows to do some custom things, for example when building .gdb_index
> looks we do not need to perform relocations computations for .debug_ranges,
> all we need is to scan relocations to find the section indexes for futher use.
>
>
> https://reviews.llvm.org/D35004
>
> Files:
>   include/llvm/DebugInfo/DIContext.h
>   lib/DebugInfo/DWARF/DWARFContext.cpp
>
>
> Index: lib/DebugInfo/DWARF/DWARFContext.cpp
> ===================================================================
> --- lib/DebugInfo/DWARF/DWARFContext.cpp
> +++ lib/DebugInfo/DWARF/DWARFContext.cpp
> @@ -1041,6 +1041,9 @@
>      if (Section.relocation_begin() == Section.relocation_end())
>        continue;
>  
> +    if (L && L->relocate(Section, Map))
> +      continue;
> +
>      // Symbol to [address, section index] cache mapping.
>      std::map<SymbolRef, SymInfo> AddrCache;
>      for (const RelocationRef &Reloc : Section.relocations()) {
> Index: include/llvm/DebugInfo/DIContext.h
> ===================================================================
> --- include/llvm/DebugInfo/DIContext.h
> +++ include/llvm/DebugInfo/DIContext.h
> @@ -16,6 +16,7 @@
>  #define LLVM_DEBUGINFO_DICONTEXT_H
>  
>  #include "llvm/ADT/SmallVector.h"
> +#include "llvm/DebugInfo/DWARF/DWARFRelocMap.h"
>  #include "llvm/Object/ObjectFile.h"
>  #include <cassert>
>  #include <cstdint>
> @@ -221,6 +222,18 @@
>      return false;
>    }
>  
> +  // Client may overload this method to perform relocations on its side.
> +  //
> +  // RelSec is a relocation section, client code is responsible for filling Map
> +  // with relocated values. It that case method should return true, to say that
> +  // client proccessed relocations and nothing else should be done on parser
> +  // side. If method returns false (default), parser is responsible for
> +  // performing relocations.
> +  virtual bool relocate(const object::SectionRef &RelSec,
> +                        RelocAddrMap *Map) const {
> +    return false;
> +  }
> +
>    /// Obtain a copy of this LoadedObjectInfo.
>    ///
>    /// The caller is responsible for deallocation once the copy is no longer required.
>
>
> Index: lib/DebugInfo/DWARF/DWARFContext.cpp
> ===================================================================
> --- lib/DebugInfo/DWARF/DWARFContext.cpp
> +++ lib/DebugInfo/DWARF/DWARFContext.cpp
> @@ -1041,6 +1041,9 @@
>      if (Section.relocation_begin() == Section.relocation_end())
>        continue;
>  
> +    if (L && L->relocate(Section, Map))
> +      continue;
> +
>      // Symbol to [address, section index] cache mapping.
>      std::map<SymbolRef, SymInfo> AddrCache;
>      for (const RelocationRef &Reloc : Section.relocations()) {
> Index: include/llvm/DebugInfo/DIContext.h
> ===================================================================
> --- include/llvm/DebugInfo/DIContext.h
> +++ include/llvm/DebugInfo/DIContext.h
> @@ -16,6 +16,7 @@
>  #define LLVM_DEBUGINFO_DICONTEXT_H
>  
>  #include "llvm/ADT/SmallVector.h"
> +#include "llvm/DebugInfo/DWARF/DWARFRelocMap.h"
>  #include "llvm/Object/ObjectFile.h"
>  #include <cassert>
>  #include <cstdint>
> @@ -221,6 +222,18 @@
>      return false;
>    }
>  
> +  // Client may overload this method to perform relocations on its side.
> +  //
> +  // RelSec is a relocation section, client code is responsible for filling Map
> +  // with relocated values. It that case method should return true, to say that
> +  // client proccessed relocations and nothing else should be done on parser
> +  // side. If method returns false (default), parser is responsible for
> +  // performing relocations.
> +  virtual bool relocate(const object::SectionRef &RelSec,
> +                        RelocAddrMap *Map) const {
> +    return false;
> +  }
> +
>    /// Obtain a copy of this LoadedObjectInfo.
>    ///
>    /// The caller is responsible for deallocation once the copy is no longer required.